Amorphous aromatic polyesters are well known in the polymeric art. They are generally characterized by the repeating unit carboxy ester ##STR1## Aromatic polyesters are of particular importance and have many useful applications. Examples of aromatic amorphous polyesters for this invention include polycarbonates, copolyestercarbonates, polyarylates and polycycloalkylene phthalates.
Generally speaking aromatic polycarbonate resins offer a high resistance to the attack of mineral acids, may be easily molded, are physiologically harmless as well as strain resistant. It is also well known that polycarbonate resins have high impact strength below a critical thickness of between about 1/8 and 1/4 inch. Additionally polycarbonates are transparent and process at relatively high temperatures with the appropriate melt viscosities.
Copolyestercarbonates are generally quite similar to polycarbonate in properties but generally have a higher secondary transition temperature (Tg) than the comparable polycarbonates. Polyarylates are generally quite similar to the copolyestercarbonates in properties but have a still higher secondary transition temperature than the copolyestercarbonates.
The uses and properties of the polycycloalkylene phthalates are well known. Common to all these amorphous aromatic polyesters are the relatively high DTUL, Distortion Temperature Under Load, as measured at a certain psig and their relatively low tensile elongation. This is also generally true with respect to blends of these amorphous polymers with polystyrenes. The presence of the polystyrene in the blends seems to bring about a relatively low tensile elongation which progressively becomes lower as increasing polystyrene is present as well as a lowering of the DTUL, a measurement of the flexural stiffness and toughness of the polymer at a specific, temperature. Once more this measurement of stiffness is lowered as the quantity of polystyrene increases in the admixture.
It has now been discovered that the addition of a graft modified polystyrene instead of a normal polystyrene tends to substantially increase the DTUL values of the polymer blends while greatly increasing the tensile elongation, particularly with the polycarbonate. Additionally it is noted that with substantially large quantities of graft modified polystyrene, the clarity of the blend is substantially higher than with the normal polystyrene molecule. Although the structure(s) of the composition is not known with certainty it is believed that ester interchange occurs to some extent between the graft modified polystyrene and the amorphous aromatic polyester, thereby forming a new molecule. It is also believed that present in the new composition is an intimate admixture of the two components.